Over the past ten years, the mass production of storage devices has become both increasingly large in scale and increasingly competitive. The combination of aggressive computer upgrade schedules, increased storage demands driven by media applications, and the opening of foreign markets to computer sales has driven up the size and scale of storage device production. However, at the same time, increased competition has driven down the cost of computer components such as storage devices. This combination of increased scale and cost-reduction pressures has increased the importance of production efficiency.
Among the tests performed during the testing of a storage device, is a head instability test. This test is intended to detect read/write heads that are prone to shifts in their magnetic fields, which can produce errors when reading the from the hard drive. Current methods of testing instability, utilize a series of high frequency shifts in the bias current (reversing the current direction every 1 or 2 cycles) that fail to fully effect the deeper layers of the read/write heads, thus allowing unstable heads to evade detection. What is needed is an improved system and method for testing that successfully excites deeper layers of the read/write head, thus allowing unstable heads to be detected.